After a young woman dressed in a ceremonial gown is found tortured and crushed beneath rocks in the Rocky Canyon, the BAU believes she is a victim of a ritualistic killing. They dig into the victim's past to learn she belonged to a utopia-type sect in town before leaving to live with her boyfriend. Canvassing the canyon leads to the remains of a second female victim. Shortly afterward, the team finds a male sexual deviant hung to death, with similar injuries as the first two victims as well as a branding on his neck. JJ notices the UnSub's tendency to remove items from the modern era from his victims and Reid analyzes the branding to identify the mark as the seal of William Stoughton, the lead prosecutor in the Salem witch trials.They determine the UnSub is emulating the execution methods used in the trials and cross-reference Stoughton's lineage with library volunteers as both of the female victims had recently frequented the library. Their search leads to Leland Duncan and his fixation with a book detailing the history of witchcraft and sorcery. He used the book to lure victims, determining that anyone who was interested in the book was guilty of being a witch. Since discovering his relation to Stoughton, Duncan had been experiencing delusions that he was condemning witches as an actual prosecutor during the Salem witch trials. Just as Duncan sets fire to a stake tied to a woman and her daughter who he believes are witches, the team steps in to take him down, rescuing the distressed pair. Afterwards, the team shares bits of each of their family histories at Garcia's Day of the Dead Halloween themed celebration.